A high-carbon nickel-based superalloy, a preparation method and application thereof

Abstract

The application belongs to the technical field of high-temperature alloys, and particularly relates to a high-carbon nickel-based high-temperature alloy and a preparation method and application thereof. The high-carbon nickel-based high-temperature alloy provided by the application contains the following components in percentage by mass: C 0.10-0.12%, Cr 17-21%, Ni 50-55%, Al 0.2-0.8%, Ti 0.65-1.15%, Zr 0.04-0.35%, Mo 2.8-3.3%, Nb 4.5-5.5%, B 0.002-0.006%, and the balance of Fe. The application reduces the proportion of Laves precipitated phase by regulating the composition of the high-carbon nickel-based high-temperature alloy, effectively controls the precipitation of the delta phase, keeps the reasonable proportion of the delta phase, reduces the size of the delta phase, refines the alloy grains, and thus improves the high-temperature mechanical properties of the high-carbon nickel-based high-temperature alloy.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature alloys, and particularly relates to a high-carbon nickel-based high-temperature alloy and a preparation method and application thereof. BACKGROUND

[0002] In recent years, with the development of the aerospace field towards lighter weight, higher flight reliability and stronger service stability design standards, advanced aero-engines have begun to widely adopt advanced structures such as precision and hollow thin-walled structures. Under this premise, the mechanical properties of the parts need to be further optimized on the basis of long-term stability, and the overall efficiency and thrust-to-weight ratio of the engine are improved to meet the demand for high-performance engines in the aerospace field.

[0003] IN718 high-temperature alloy is a kind of metal material with good oxidation resistance and corrosion resistance, excellent mechanical properties, and good cold and hot working properties, which is widely used in hot end components of aero-engines and space engines. Under high-temperature service environment, these components need to withstand complex stress states, including long-term high-temperature steady stress, frequent thermal cycle stress and complex mechanical load. Although IN718 high-temperature alloy exhibits satisfactory mechanical properties at room temperature. But under higher temperature long-time service, if the proportion of Laves phase in the alloy is high, the size and proportion of δ phase after heat treatment are difficult to control effectively, which may affect the stability of the grain boundary and is not conducive to enhancing the deformation resistance of the alloy at high temperature. In addition, defects such as shrinkage and porosity will become the source of crack initiation and propagation at high temperature, which will also reduce the high-temperature reliability of the material. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a high-carbon nickel-based high-temperature alloy and a preparation method and application thereof, which has a small proportion of Laves precipitated phase, a moderate proportion and small size of δ phase after heat treatment, refined alloy grain and low porosity, so as to have excellent high-temperature mechanical properties.

[0005] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0006] The present application provides a high-carbon nickel-based high-temperature alloy, which comprises the following components in mass percentage: C 0.10-0.12%, Cr 17-21%, Ni 50-55%, Al 0.2-0.8%, Ti 0.65-1.15%, Zr 0.04-0.35%, Mo 2.8-3.3%, Nb 4.5-5.5%, B 0.002-0.006%, and the balance is Fe.

[0007] The volume fraction of the delta phase in the high-carbon nickel-based superalloy is 2-2.4%, the average size of the delta phase is 6.6-7.8 μm, the volume fraction of the Laves precipitated phase is 1.7-1.9%, the volume fraction of the carbide precipitated phase is 1.48-2.17%, and the average distribution interval between the carbide precipitated phases is 24±8 μm.

[0008] The porosity of the high-carbon nickel-based superalloy is ≤1%, and the grain size of the alloy is 78-118 μm.

[0009] Preferably, the matrix structure of the high-carbon nickel-based superalloy is composed of face-centered cubic austenite phases of nickel, iron and chromium, with a volume fraction of 70-80%, the main component of the main strengthening phase is Ni3Nb, with a volume fraction of 10-20%, and the main component of the secondary strengthening phase is Ni3Al, with a volume fraction of 1-3%.

[0010] The application also provides a preparation method of the high-carbon nickel-based superalloy.

[0011] After the high-carbon nickel-based alloy ingot is subjected to rough refining and refining in sequence under vacuum, the obtained melt is poured into a mold shell to perform directional thermal controlled solidification, so as to obtain a solidified alloy; the element composition of the high-carbon nickel-based alloy ingot is the same as that of the high-carbon nickel-based superalloy.

[0012] After the solidified alloy is cooled to room temperature, the high-carbon nickel-based superalloy is obtained by performing uniformization heat treatment, solid solution heat treatment and aging heat treatment in sequence.

[0013] Preferably, the directional thermal controlled solidification is to draw the mold shell containing the melt from a hot zone to a cold zone, to perform slow cooling in the hot zone and to perform rapid cooling in the cold zone; the temperature of the hot zone is 1290-1300 ℃; the temperature of the cold zone is 100-300 ℃; the cooling rate of the slow cooling in the hot zone is 0.16-0.18 ℃ / s; and the cooling rate of the rapid cooling in the cold zone is 5-10 ℃ / s.

[0014] Preferably, the rough refining is to increase the temperature from room temperature to 1400-1600 ℃, and the temperature increasing time is 20-40 min; and the refining is to keep the temperature at 1500-1600 ℃ for 2-4 min.

[0015] Preferably, before the pouring, the method further comprises: preheating the mold shell; the preheating temperature of the mold shell is 1290-1300 ℃; and the pouring speed is 0.5-0.8 kg / s.

[0016] Preferably, the temperature of the uniformization heat treatment is 1050-1150 ℃, and the holding time is 1.5-2.5 h.

[0017] Preferably, the temperature of the solid solution heat treatment is 950-955 DEG C, and the holding time is 1.5-2 h.

[0018] Preferably, the aging heat treatment is: first, first-stage aging heat treatment is performed, then first cooling is performed, second-stage aging heat treatment is performed, and finally second cooling is performed to room temperature; the temperature of the first-stage aging heat treatment is 720-730 DEG C, and the holding time is 7-8 h; the first cooling rate is 50-56 DEG C / h; the temperature of the second-stage aging heat treatment is 620-630 DEG C, and the holding time is 7-8 h; and the second cooling rate is 40-50 DEG C / min.

[0019] The application further provides application of the high-carbon nickel-based high-temperature alloy or the high-carbon nickel-based high-temperature alloy prepared by the preparation method in aerospace components.

[0020] The application provides a high-carbon nickel-based high-temperature alloy, which comprises the following components in percentage by mass: C 0.10-0.12%, Cr 17-21%, Ni 50-55%, Al 0.2-0.8%, Ti 0.65-1.15%, Zr 0.04-0.35%, Mo 2.8-3.3%, Nb 4.5-5.5%, B 0.002-0.006%, and the balance of Fe; the volume fraction of a delta phase in the high-carbon nickel-based high-temperature alloy is 2-2.4%, the average size of the delta phase is 6.6-7.8 mu m, the volume fraction of a Laves precipitated phase is 1.7-1.9%, the volume fraction of a carbide precipitated phase is 1.48-2.17%, and the average distribution interval between the carbide precipitated phases is 24+8 mu m; the porosity of the high-carbon nickel-based high-temperature alloy is less than or equal to 1%, and the grain size of the alloy is 78-118 mu m. By adjusting the composition of the high-carbon nickel-based high-temperature alloy, the content of C is increased to reduce the proportion of the Laves precipitated phase, the precipitation of the delta phase is effectively controlled, the proportion of the delta phase is reasonably maintained, the size of the delta phase is reduced, the porosity is reduced, the grain of the alloy is refined, the density is improved, internal defects are reduced, the grain boundary (interface between grains) structure is stable, the alloy failure mechanism caused by grain boundary diffusion and grain boundary sliding under high temperature can be more effectively resisted, the high-temperature creep resistance and high-temperature strength are improved, and therefore the high-temperature mechanical properties of the high-carbon nickel-based high-temperature alloy are improved.

[0021] The application also provides a preparation method of the high-carbon nickel-based superalloy. The application adjusts the alloy melt characteristics of trace elements (carbon elements), and uses a new heat control solidification method, which not only meets the requirement of low porosity, but also guarantees that the high-carbon nickel-based superalloy has good high-temperature mechanical properties. The interdendritic liquid phase channel is kept for a long time under the new heat control solidification method (MTCS), the melt is more easily to be top-up, the porosity of the high-carbon nickel-based superalloy is significantly reduced, and meanwhile, all elements are fully diffused, migrated and distributed. Simulation and experiment show that the carbide precipitation sequence is before the Laves precipitated phase, and the precipitation of the carbide mainly containing NbC consumes a considerable proportion of Nb atoms, which leads to the reduction of the proportion of the solidified Laves precipitated phase. The thermal stability of NbC is strong and it is not easy to dissolve, and a large amount of Nb is not released in the subsequent process, so it is difficult to form a Nb-rich region. Without the Nb-rich region, there is a lack of a large amount of Nb element source which can promote the nucleation and growth of the δ phase, so that the amount and size of the δ phase precipitated in the high-carbon nickel-based superalloy after aging heat treatment are moderate, the alloy grain is refined, and the morphology of the grain boundary is effectively regulated. The high C content increases the carbide precipitation temperature, and the slow cooling rate provides sufficient space for the growth and development of the carbide in the high-carbon nickel-based superalloy melt. During this period, the Ostwald ripening phenomenon occurs, the large carbide further grows, and the small carbide dissolves, so that the density of the carbide on the grain boundary is not too high. Due to the pinning effect of the carbide, the increase of the carbide also hinders the grain boundary migration and inhibits the grain coarsening, so that the grain is more fine. The fine-grained structure increases the number and area of the grain boundaries, and the grain boundaries can hinder the movement of dislocations. When the number of grain boundaries increases, the dislocations will encounter more obstacles in the movement process, which makes the alloy more difficult to deform. Therefore, the strengthening of the number and area of the grain boundaries can consume the energy required for crack propagation and prolong the time required for hole connection, thereby effectively improving the high-temperature strength of the high-carbon nickel-based superalloy. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Creep rupture life diagram of the high-carbon nickel-based superalloy prepared in Example 1-3 and the nickel-based superalloy prepared in Comparative Example 3;

[0023] Figure 2 Creep rupture life diagram of the high-carbon nickel-based superalloy prepared in Example 1 (MTCS), the alloy castings prepared in Comparative Example 1 (CC), Comparative Example 2 (CGC) and Comparative Example 3;

[0024] Figure 3 XRD diagram of the alloy casting prepared in Comparative Example 1 by using the ordinary casting method;

[0025] Figure 4 XRD diagram of the high-carbon nickel-based superalloy prepared in Example 1;

[0026] Figure 5 Microstructure analysis chart of the high-carbon nickel-based superalloy prepared in Example 1;

[0027] Figure 6 Microstructure analysis chart of the alloy cast prepared in Comparative Example 1 by the common casting method;

[0028] Figure 7 As-cast microstructure analysis chart of the high-carbon nickel-based superalloy prepared in Example 1;

[0029] Figure 8 Heat treatment microstructure analysis chart of the high-carbon nickel-based superalloy prepared in Example 1;

[0030] Figure 9 As-cast microstructure analysis chart of the alloy cast prepared in Comparative Example 1 by the common casting method;

[0031] Figure 10 Heat treatment microstructure analysis chart of the alloy cast prepared in Comparative Example 1 by the common casting method;

[0032] Figure 11 As-cast microstructure analysis chart of the nickel-based superalloy prepared in Comparative Example 3;

[0033] Figure 12 Heat treatment microstructure analysis chart of the nickel-based superalloy prepared in Comparative Example 3. DETAILED DESCRIPTION

[0034] The present application provides a high-carbon nickel-based superalloy, comprising the following components in mass percentage: C 0.10-0.12%, Cr 17-21%, Ni 50-55%, Al 0.2-0.8%, Ti 0.65-1.15%, Zr 0.04-0.35%, Mo 2.8-3.3%, Nb 4.5-5.5%, B 0.002-0.006%, and the balance of Fe;

[0035] The volume fraction of the δ phase in the high-carbon nickel-based superalloy is 2-2.4%, the average size of the δ phase is 6.6-7.8 μm, the volume fraction of the Laves precipitated phase is 1.7-1.9%, the volume fraction of the carbide precipitated phase is 1.48-2.17%, and the average distribution interval between the carbide precipitated phases is 24±8 μm;

[0036] The porosity of the high-carbon nickel-based superalloy is ≤1%, and the grain size of the alloy is 78-118 μm.

[0037] Unless otherwise specified, the present application does not have special requirements for the source of the raw materials used, and commercially available goods known to those skilled in the art can be used.

[0038] As an implementation form, the high-carbon nickel-based superalloy comprises the following components in mass percentage: C 0.10-0.12%, Cr 19.50%, Ni 52.97%, Al 0.44%, Ti 0.94%, Zr 0.32%, Mo 3.09%, Nb 4.99%, B 0.0029%, and the balance being Fe.

[0039] As an implementation form, the mass percentage of C in the high-carbon nickel-based superalloy is 0.10%, 0.11% or 0.12%, and in a specific embodiment, 0.12%.

[0040] The increase of C content in the present application can reduce the proportion of Laves precipitated phase in the high-carbon nickel-based superalloy. The high C content increases the carbide precipitation temperature, and the slow cooling rate provides sufficient space for the growth and development of carbides in the high-carbon nickel-based superalloy melt. During this period, the Ostwald ripening phenomenon occurs, the large carbides further grow, and the small carbides dissolve, so that the density of carbides on the grain boundary is not too high. The increase of carbides also hinders the grain boundary migration and inhibits the grain coarsening. The fine-grained structure obtained increases the number and area of grain boundaries, and the grain boundaries can hinder the movement of dislocations. When the number of grain boundaries increases, the dislocations will encounter more obstacles during movement, which makes the alloy more difficult to deform. Therefore, the strengthening of the number and area of grain boundaries can consume the energy required for crack propagation and prolong the time required for hole connection, thereby effectively improving the high-temperature strength of the high-carbon nickel-based superalloy.

[0041] As an implementation form, the high-carbon nickel-based superalloy further comprises impurity elements in a mass percentage of ≤0.01%, and the impurity elements include H, O, V, P and Mn.

[0042] As an implementation form, the porosity of the high-carbon nickel-based superalloy is ≤1%, and in a specific embodiment, 0.05-1%; the grain size of the alloy is 78-118 μm, and in a specific embodiment, 98 μm.

[0043] As an implementation form, the volume fraction of δ phase in the high-carbon nickel-based superalloy is 2-2.4%, and in a specific embodiment, 2.5%; the average size of δ phase is 6.6-7.8 μm, and in a specific embodiment, 7.2 μm; the volume fraction of Laves precipitated phase is 1.7-1.9%, and in a specific embodiment, 1.8%; the volume fraction of carbide precipitated phase is 1.48-2.17%, and the average distribution distance between carbide precipitated phases is 24±8 μm, and in a specific embodiment, 24 μm.

[0044] As an embodiment, the high-carbon nickel-based superalloy has a matrix structure of face-centered cubic austenite phase composed of nickel, iron and chromium, with a volume fraction of 70-80%, a main strengthening phase mainly composed of Ni3Nb, with a volume fraction of 10-20%, and a secondary strengthening phase mainly composed of NbC, with a volume fraction of 1-3%.

[0045] As an embodiment, the high-carbon nickel-based superalloy includes a matrix structure (γ phase), a main strengthening phase (γ" phase), a secondary strengthening phase (γ' phase), a carbide precipitate phase (MC), a Laves precipitate phase and a δ phase.

[0046] As an embodiment, the matrix structure is a basic structure of face-centered cubic austenite phase composed of nickel (Ni), iron (Fe) and chromium (Cr). The matrix structure gives the high-carbon nickel-based superalloy good toughness and certain high-temperature stability.

[0047] As an embodiment, the main strengthening phase (γ" phase) is mainly composed of Ni3Nb, and the γ" phase is a body-centered tetragonal structure (D022). The γ" phase is the most important strengthening phase in the high-carbon nickel-based superalloy. The ordered body-centered tetragonal structure has a specific orientation relationship with the austenite matrix, and its existence can effectively hinder dislocation movement, thereby improving the strength and creep resistance of the high-carbon nickel-based superalloy.

[0048] As an embodiment, the secondary strengthening phase (γ' phase) is mainly composed of Ni3Al, and the γ' phase is a face-centered cubic structure.

[0049] As an embodiment, the carbide precipitate phase (MC) is mainly composed of NbC and has a face-centered cubic structure. The carbide precipitate phase precipitates at grain boundaries and hinders dislocation movement.

[0050] As an embodiment, the Laves precipitate phase is of A2B type and mainly composed of Fe2Nb. The Laves precipitate phase is a complex topological close-packed phase, which is in a close-packed hexagonal (C14) structure in the high-carbon nickel-based superalloy. It is a brittle phase and has certain influence on plasticity and high-temperature strength, and needs to be reasonably controlled.

[0051] As an embodiment, the δ phase is mainly composed of Ni3Nb, and the δ phase is a body-centered orthorhombic structure (D0a). In addition to the precipitation in the Nb-rich region during heat treatment, the intracrystalline metastable strengthening phase γ" phase will transform into the stable δ phase under the condition of high-temperature use at more than 650°C. The number and size of the phase will affect the plasticity and toughness and high-temperature strength of the high-carbon nickel-based superalloy.

[0052] The application effectively controls the precipitation of the delta phase by regulating the composition of the high-carbon nickel-based superalloy, so that the delta phase maintains a reasonable grain size and distribution, thereby improving the high-temperature mechanical properties of the high-carbon nickel-based superalloy.

[0053] The application also provides a preparation method of the high-carbon nickel-based superalloy.

[0054] The high-carbon nickel-based alloy ingot is subjected to rough refining and refining under vacuum conditions, and then the obtained melt is poured into a mold shell to perform directional heat-controlled solidification to obtain a solidified alloy.

[0055] After the solidified alloy is cooled to room temperature, it is subjected to uniform heat treatment, solid solution heat treatment and aging heat treatment in sequence to obtain the high-carbon nickel-based superalloy.

[0056] The application performs rough refining and refining on a high-carbon nickel-based alloy ingot under vacuum conditions, pours the obtained melt into a mold shell to perform directional heat-controlled solidification to obtain a solidified alloy.

[0057] As an embodiment, the preparation method of the high-carbon nickel-based alloy ingot is to entrust Jiangsu Longda Super Alloy Co., Ltd. to cast according to the component content of the high-carbon nickel-based superalloy.

[0058] As an embodiment, the vacuum pressure of the vacuum condition is (5-10) x 10 -3 MPa, and in a specific embodiment, it is 5 x 10 -3 MPa; the rough refining, refining, pouring and directional heat-controlled solidification are all performed in an HRS directional solidification furnace.

[0059] As an embodiment, the rough refining is to heat from room temperature to 1400-1600℃, and in a specific embodiment, it is 1500℃, and the heating time is 20-40 min, and in a specific embodiment, it is 30 min; the refining is to keep at 1500-1600℃ for 2-4 min, and in a specific embodiment, it is to keep at 1550℃ for 2-3 min.

[0060] As an implementation form, before the pouring, the mold shell is preheated, and the preheating temperature of the mold shell is 1290-1300 DEG C, and in a specific embodiment, the preheating temperature is 1295 DEG C. Before the pouring, the melt is cooled to 1360 DEG C, and the cooling rate is 50 DEG C / min. The pouring rate is 0.5-0.8 kg / s, and in a specific embodiment, the pouring rate is 0.6-0.7 kg / s. In the present application, the temperature of the mold shell is set in the above range, which helps to reduce the temperature loss of the melt during pouring, improve the fluidity and reduce the defect generation. During the pouring process, the stability and sealing of the pouring system are maintained to prevent air absorption and oxidation.

[0061] As an implementation form, the directional heat control solidification is to pull the mold shell containing the melt from a hot zone to a cold zone, slow cooling in the hot zone, and rapid cooling in the cold zone. The temperature of the hot zone is 1290-1300 DEG C, and in a specific embodiment, the temperature of the hot zone is 1295 DEG C. The temperature of the cold zone is 100-300 DEG C, and in a specific embodiment, the temperature of the cold zone is 200 DEG C. The slow cooling rate in the hot zone is 0.16-0.18 DEG C / s, and in a specific embodiment, the slow cooling rate is 0.17-0.18 DEG C / s. The rapid cooling rate in the cold zone is 5-10 DEG C / s, and in a specific embodiment, the rapid cooling rate is 8-10 DEG C / s.

[0062] In the present application, the hot zone generally refers to the initial region of the mold shell after the melt is poured into the mold shell, such as a crucible, and a high-power graphite heating element is used to ensure that the melt is in a semi-solid state for a short time and maintains the dendritic channel, which is beneficial to the control and stability of the initial solidification process. The cold zone generally refers to the region inside the furnace body away from the hot zone, which is controlled by a circulating water cooling system, a vacuum system, and the like to reduce convective heat transfer, so as to ensure that there is a temperature gradient between the cold zone and the hot zone, guide the melt to directional solidification along the set direction, and thus obtain a directional solidification structure with specific organization and performance.

[0063] In the present application, "pulling" refers to moving the pulling rod from the hot zone to the cold zone at the above pulling speed by controlling the panel and the motor. Within the above pulling speed range, the problem of poor feeding and deteriorated mechanical properties caused by too fast cooling speed due to too fast pulling speed can be avoided, and the problem of coarse grain growth and deteriorated mechanical properties caused by too slow pulling speed can also be avoided.

[0064] After obtaining the solidified alloy, the solidified alloy is cooled to room temperature, and then subjected to homogenization heat treatment, solid solution heat treatment and aging heat treatment in sequence to obtain the high-carbon nickel-based superalloy.

[0065] As an implementation form, after the solidified alloy is cooled to room temperature, the mold shell is removed. The present application does not have special limitations on the way of removing the mold shell, and a way well known in the art can be used.

[0066] As an implementation form, the homogenization heat treatment, the solution heat treatment and the aging heat treatment are all carried out in air.

[0067] As an implementation form, the temperature of the homogenization heat treatment is 1050-1150℃, and in particular embodiments, it is 1100℃, the holding time is 1.5-2.5h, and in particular embodiments, it is 2h; the heating rate from room temperature to the temperature of the homogenization heat treatment is 5-10℃ / min, and in particular embodiments, it is 5.5-7.5℃ / min. In the present application, the homogenization heat treatment is a process of using atomic diffusion to make alloy elements uniformly distributed in the alloy, reduce segregation, make the structure more uniform, and release residual stress at the same time in a long time holding at high temperature.

[0068] As an implementation form, before the solution heat treatment, the method further comprises: rapidly cooling the solidified alloy after the homogenization heat treatment to room temperature in air; the rapid cooling rate is 40-50℃ / min, and in particular embodiments, it is 45-50℃ / min.

[0069] As an implementation form, the temperature of the solution heat treatment is 950-955℃, and in particular embodiments, it is 955℃, the holding time is 1.5-2h, and in particular embodiments, it is 2h; the heating rate from room temperature to the temperature of the solution heat treatment is 8-12℃ / min, and in particular embodiments, it is 9-10℃ / min. In the present application, the solution heat treatment is to heat the alloy to a high temperature to dissolve the second phase to form a supersaturated solid solution. At this temperature, the alloy elements diffuse sufficiently, the alloy matrix composition is further uniform, and the supersaturated alloy matrix is prepared for the subsequent aging heat treatment, and the processing performance is improved at the same time.

[0070] As an implementation form, before the aging heat treatment, the method further comprises: rapidly cooling the solidified alloy after the solution heat treatment to room temperature in air; the rapid cooling rate is 40-50℃ / min, and in particular embodiments, it is 45-50℃ / min.

[0071] As an implementation, the aging heat treatment is: first, a first stage aging heat treatment is performed, then a first cooling is performed, a second stage aging heat treatment is performed, and finally a second cooling is performed to room temperature; the temperature of the first stage aging heat treatment is 720-730℃, and in a specific embodiment, the temperature is 725℃, and the holding time is 7-8h; the rate of the first cooling is 50-56℃ / h; the temperature of the second stage aging heat treatment is 620-630℃, and in a specific embodiment, the temperature is 620-625℃, and the holding time is 7-8h; the rate of the second cooling is 40-50℃ / min, and in a specific embodiment, the rate is 50℃ / min; the rate of heating from room temperature to the temperature of the first stage aging heat treatment is 8-10℃ / min, and in a specific embodiment, the rate is 9℃ / min. In the present application, the aging heat treatment is performed on the supersaturated solid solution after the solid solution heat treatment, the temperature is lowered to make the solute atoms precipitate in the form of fine dispersed strengthening phases (such as γ', γ''), these strengthening phases hinder the movement of dislocations, and by controlling the parameters of the aging heat treatment, the size and distribution of the precipitated phases are adjusted, thereby improving the strength and hardness of the high-carbon nickel-based high-temperature alloy.

[0072] By adjusting the trace elements (carbon elements) on the existing mature IN718 high-temperature alloy, the distribution and state of the precipitated phases are improved, and the grain boundary strengthening effect is improved, which not only improves the comprehensive performance of the material, but also maximizes the development cost and shortens the technical transformation cycle. However, it is difficult to manufacture large-size complex thin-walled casting of machine cases with complete structure and excellent performance by conventional casting methods, and the combined effect of melt characteristics and thin-walled effect easily causes large shrinkage holes or even underfilling in the casting. If the method of increasing the pouring temperature is adopted to improve the filling effect, the casting will produce coarse grains or through grains, resulting in a sharp decay of high-temperature strength. In the present application, the solidification characteristics of the alloy are simulated and calculated by using Pandat software, and it is found that increasing the C content can reduce the proportion of Laves precipitated phase in the high-carbon nickel-based high-temperature alloy, and the Laves precipitated phase and the surrounding area is often rich in Nb, but a large number of Nb atoms released after heat treatment will accelerate the precipitation and growth of δ phase. At present, in the conventional casting, ① the increase of C content only increases the number and size of carbides, and does not significantly reduce the proportion of Laves phase in the alloy, because the growth and contact of coarse dendrites isolate the interdendritic liquid phase quickly, and at this time, the diffusion of Nb atoms through the solid-liquid interface is difficult, so the influence on the formation of Laves is relatively small. ② The large-size interdendritic carbides formed by the increase of C content will cause difficulty in interdendritic liquid phase feeding during the conventional casting process, so the porosity of the alloy will increase sharply when the C content is at a high level, and the filling capacity and filling quality will decrease.

[0073] The present application is directed to the alloy melt characteristics of trace elements (carbon element) adjustment, the new heat control solidification method is used in matched mode, both meet the requirements of low porosity, and can guarantee that the high carbon nickel-based superalloy has good high temperature mechanical properties. The interdendritic liquid phase channel remains for a long time under the new heat control solidification method (MTCS), the melt is more prone to feeding, the porosity of the high carbon nickel-based superalloy is significantly reduced, and the elements can be fully diffused, migrated and distributed. Simulation and experiment show that the carbide precipitation sequence is before the Laves precipitated phase, and the precipitation of the carbide mainly containing NbC consumes a considerable proportion of Nb atoms, which leads to a reduced proportion of the solidified Laves precipitated phase. The thermal stability of NbC is strong and it is not easy to dissolve, and a large amount of Nb is not released during the subsequent heat treatment, so it is difficult to form a Nb-rich region. Without the Nb-rich region, a large amount of Nb element source which can promote the nucleation and growth of the delta phase is lacking, so that the amount of the delta phase precipitated by the high carbon nickel-based superalloy after aging heat treatment is small, the grain size is small, and the morphology of the grain boundary is effectively controlled. The high C content increases the carbide precipitation temperature, and the slow cooling rate provides sufficient space for the growth and development of the carbide in the high carbon nickel-based superalloy melt. During this period, the Ostwald ripening phenomenon occurs, the large carbide further grows, and the small carbide dissolves, so that the density of the carbide on the grain boundary is not too high. The increase of the carbide also hinders the grain boundary migration and inhibits the grain coarsening. The fine-grained structure increases the number and area of the grain boundaries, and finally effectively improves the high temperature strength of the high carbon nickel-based superalloy. Therefore, although the carbon content in the high carbon nickel-based superalloy is at a high level, the porosity of the high carbon nickel-based superalloy prepared by the preparation method is relatively lower than that prepared by the conventional casting method. At the same time, due to the pinning effect of the carbide, the grain boundary migration is hindered, which makes the grain smaller. The size and number of the delta phase and the carbide at the grain boundary are effectively controlled, and the high temperature mechanical properties of the alloy are greatly improved. Under the conditions of slow and sequential solidification, the carbide precipitated first combines with a large amount of Nb atoms, and the proportion of the Laves phase produced during the final solidification is significantly reduced. The reduction of the Nb-rich region reduces the delta phase precipitated after heat treatment, and the grain boundary precipitated phase state is effectively controlled.

[0074] The present application also provides the application of the high carbon nickel-based superalloy prepared by the preparation method in aerospace components.

[0075] The application mode of the high carbon nickel-based superalloy in aerospace components is not specially limited in the present application, and the application mode known in the art can be used.

[0076] The technical solutions in the present application will be clearly and completely described below in combination with the embodiments in the present application, but they should not be understood as limitations to the protection scope of the present application.

[0077] Examples 1-3

[0078] The components of the high-carbon nickel-based superalloy in Example 1 are, in mass percentage: Cr 19.50%, Ni 52.97%, Al 0.44%, Ti 0.94%, Zr 0.32%, Mo 3.09%, Nb 4.99%, C 0.12%, B 0.0029%, Fe balance, impurities (H, O, V, P and Mn) ≤0.01%;

[0079] The specific preparation process is as follows: a test rod shell with a base diameter of 60 mm and a height of 190 mm is heated to 1290℃ by a graphite heating body in an HRS directional solidification furnace and is kept for 2 h, a high-carbon nickel-based superalloy ingot cast by Jiangsu Longda Super Alloy Co., Ltd. according to the component content of the high-carbon nickel-based superalloy is placed in a crucible of the HRS directional solidification furnace with a vacuum pressure of 5×10 -3 MPa, is heated from room temperature to 1500℃ within 30 min for roughing, after the high-carbon nickel-based superalloy ingot is completely melted, heating is stopped for 40 s, then the temperature is raised to 1550℃ and kept for 2 min for refining, so that the alloy composition is more uniform and impurity gases are discharged, then the obtained melt is cooled to 1360℃ at a speed of 50℃ / min, and is poured into the test rod shell preheated to 1290℃ at a speed of 0.5 kg / s, directional thermal control solidification is realized by pulling the test rod shell from the hot zone (1295℃) to the cold zone (200℃), the temperature is slowly reduced at a speed of 0.18℃ / s in the hot zone, after the test rod shell is pulled away from the hot zone, it is rapidly cooled at a speed of 10℃ / s in the cold zone, after the test rod shell is naturally cooled to room temperature, the test rod shell is knocked open, the cooled solidified alloy is taken out, and is placed in a heat treatment furnace to sequentially perform homogenization heat treatment, solid solution heat treatment and aging heat treatment in air, the homogenization heat treatment is performed by raising the temperature from room temperature to 1100℃ at a speed of 7.5℃ / min and keeping for 2 h, then rapidly cooling to room temperature at a speed of 50℃ / min in air; the solid solution heat treatment is performed by raising the temperature from room temperature to 955℃ at a speed of 10℃ / min and keeping for 1.5 h, then rapidly cooling to room temperature at a speed of 50℃ / min in air; the aging heat treatment is performed by first raising the temperature from room temperature to 720℃ at a speed of 9℃ / min and keeping for 8 h, then reducing the temperature to 620℃ at a speed of 50℃ / h and keeping for 8 h, then rapidly cooling to room temperature at a speed of 50℃ / min in air, to obtain the high-carbon nickel-based superalloy.

[0080] Example 2

[0081] The difference from Example 1 is that the mass percentage of C in the components of the high-carbon nickel-based superalloy is 0.10%.

[0082] Example 3

[0083] The difference from Example 1 is that the mass percentage of C in the high-carbon nickel-based superalloy is 0.11%.

[0084] Comparative Example 1

[0085] The difference from Example 1 is that it is prepared using conventional casting (CC) method. The specific preparation process is as follows: a vacuum induction melting furnace is used at a vacuum pressure of 2×10⁻⁶. -2 The alloy ingot cast according to the composition of the high-carbon nickel-based high-temperature alloy in Example 1 was melted at Pa and 1450℃ for 1 hour. The resulting melt was poured into a mold shell held at 900℃ at a speed of 0.5 kg / s. After the melt solidified and cooled to room temperature in the mold shell, the mold shell was removed, and the resulting casting was cleaned and polished to remove surface impurities (adhering sand, oxide scale) to obtain the alloy casting.

[0086] Comparative Example 2

[0087] The difference from Example 1 is that the IN718 high-temperature alloy (with a carbon content of 0.05% by mass) was prepared using counter-gravity casting (CGC). The specific preparation process is as follows: The raw materials for the IN718 alloy were precisely prepared and pretreated to remove impurities. The raw materials were placed in an induction furnace and argon gas was introduced at a flow rate of 20 L / min. Melting was carried out at 1500°C for 2 hours. The melt temperature was stabilized within the range of 1400–1450°C. The counter-gravity casting equipment was started, and the pressure difference (i.e., holding pressure 0–180 kPa) was precisely adjusted at a pouring speed of 5 kg / s. The molten material is slowly poured from bottom to top into a ceramic mold preheated to 900°C under the action of anti-gravity. During pouring, the mold transfer time is kept constant at 5 min, the alloy temperature at 1400°C, the mold preheating temperature at 1050°C, the argon flow rate in the furnace at 10 L / min, and the residence time in the ceramic mold at 5 s. At the same time, the slag on the surface of the molten material between the continuous casting molds is removed to ensure stable and high-quality pouring. After the molten material solidifies and cools to room temperature in the mold shell, the mold shell is removed, and the resulting casting is cleaned and polished to remove surface impurities (adhering sand, oxide scale) to obtain the alloy casting.

[0088] Comparative Example 3

[0089] The difference from Example 1 is that the mass percentage of C in the nickel-based superalloy is 0.06%.

[0090] Performance testing

[0091] (1) The high-carbon nickel-based superalloys prepared in Examples 1-3 and the nickel-based superalloy prepared in Comparative Example 3 were processed into circular rod-shaped specimens (the gauge length of the mechanical specimen was 25 mm, and the cross-sectional diameter was 5 mm). Creep tests at 650℃ / 620MPa were conducted on a SATEC M3 testing machine to analyze and evaluate their high-temperature mechanical properties. The results are as follows: Figure 1 As shown, 0.12C, 0.10C, and 0.11C represent the high-carbon nickel-based superalloys prepared in Examples 1 to 3, respectively, and 0.06C represents the nickel-based superalloy prepared in Comparative Example 3.

[0092] Depend on Figure 1 It can be seen that the creep rupture lifetimes of the high-carbon nickel-based superalloys prepared in Examples 1-3 at 650℃ / 620MPa were 328.9h, 247.6h and 293.5h, respectively, while the creep rupture lifetime of the nickel-based superalloy prepared in Comparative Example 3 at 650℃ / 620MPa was 176.7h. It is evident that increasing the mass percentage of C element in the high-carbon nickel-based superalloy can enhance the creep rupture lifetime.

[0093] (2) The high-carbon nickel-based superalloy (MTCS) prepared in Example 1, the alloy casting (CC) prepared in Comparative Example 1, the alloy casting (CGC) prepared in Comparative Example 2, and the nickel-based superalloy prepared in Comparative Example 3 were subjected to a creep test at 650℃ / 620MPa on a SATEC M3 testing machine. The results are as follows: Figure 2 As shown, Standard represents aviation standards.

[0094] Depend on Figure 2 It can be seen that the creep rupture lives of the high-carbon nickel-based superalloy (MTCS) prepared in Example 1, the alloy casting (CC) prepared by conventional casting method in Comparative Example 1, the alloy casting (CGC) prepared by anti-gravity casting method in Comparative Example 2, and the nickel-based superalloy prepared in Comparative Example 3 at 650℃ / 620MPa are 328.9h, 87.0h, 95.4h, and 176.7h, respectively. Although the creep rupture lives of these four alloy materials are all higher than the aerospace standard (26.2h), the creep rupture life of the high-carbon nickel-based superalloy prepared by this invention is much higher than that of the alloy castings prepared by conventional casting method and anti-gravity casting method. This indicates that the high-carbon nickel-based superalloy prepared by this invention has excellent high-temperature mechanical properties.

[0095] (3) Figure 3 The image shows the XRD pattern of the alloy casting prepared by the conventional casting method in Comparative Example 1. Figure 4 The image shows the XRD pattern of the high-carbon nickel-based superalloy prepared in Example 1.

[0096] Depend on Figure 3It can be seen that the alloy casting prepared by the ordinary casting method contains carbides, mainly NbC, and a small amount of TiC peak. The carbide peak is relatively low, and the peak area is relatively small, so the amount of carbide precipitation in the alloy casting is relatively small.

[0097] By Figure 4 It can be seen that the high-carbon nickel-based superalloy prepared in Example 1 contains carbides, mainly NbC, and a small amount of TiC peak. Compared with the alloy casting prepared by the ordinary casting method in Comparative Example 1, the carbide peak of the high-carbon nickel-based superalloy prepared in Example 1 is higher, and the peak area is relatively larger, so the amount of carbide precipitation in the high-carbon nickel-based superalloy prepared in Example 1 is relatively high, and the peak signal of δ phase is weakened, which is considered to be due to the decrease of the content of δ phase. Figure 3

[0098] (4) Figure 5 Figure 4 is a metallographic structure analysis diagram of the high-carbon nickel-based superalloy prepared in Example 1, Figure 6 Figure 5 is a metallographic structure analysis diagram of the alloy casting prepared by the ordinary casting method in Comparative Example 1.

[0099] Comparing Figure 5 and Figure 6 It can be seen that the porosity of the high-carbon nickel-based superalloy prepared in Example 1 is in the range of 0.05-1%, and the porosity of the alloy casting prepared by the ordinary casting method in Comparative Example 1 is in the range of 1-5%. It can be seen that when the mass percentage of C in the alloy is increased to 0.12%, the porosity is relatively high under the conventional casting (CC) method because the precipitation of a large amount of carbides hinders the feeding of the melt. However, under the new heat control solidification method used in the present application, a higher and more stable mold shell temperature is maintained to maintain more liquid phase, and the solidification under this method is orderly promoted, which can ensure that the liquid metal smoothly fills the volume vacancy caused by solidification shrinkage under the action of pressure difference through the interdendritic liquid phase channel. This method effectively feeds the high-carbon nickel-based superalloy, which significantly reduces the porosity of the high-carbon nickel-based superalloy, and further improves the density and mechanical properties of the high-carbon nickel-based superalloy.

[0100] (5) Figure 7 Figure 6 is a cast structure analysis diagram of the high-carbon nickel-based superalloy prepared in Example 1, Figure 8 Figure 7 is a heat treatment structure analysis diagram of the high-carbon nickel-based superalloy prepared in Example 1, Figure 9 Figure 8 is a cast structure analysis diagram of the alloy casting prepared by the ordinary casting method in Comparative Example 1, Figure 10 Figure 9 is a heat treatment structure analysis diagram of the alloy casting prepared by the ordinary casting method in Comparative Example 1.

[0101] Comparing Figure 7 and Figure 9 ​It can be seen that the volume fraction of Laves precipitated phase of the high-carbon nickel-based superalloy prepared in Example 1 is only 1.8±0.1%, while the volume fraction of Laves precipitated phase of the alloy casting prepared by the ordinary casting method in Comparative Example 1 is 15.7±1.1%, so compared with Comparative Example 1, the volume fraction of Laves precipitated phase of the high-carbon nickel-based superalloy prepared by the new heat-controlled solidification method in the application is low, and the Nb-rich region near the Laves precipitated phase is also less.

[0102] Comparison Figure 8 and Figure 10 It can be seen that the volume fraction of δ phase of the high-carbon nickel-based superalloy prepared in Example 1 is 2.2±0.2%, and the average size of δ phase is about 7.2±0.6μm, while the volume fraction of δ phase of the alloy casting prepared by the ordinary casting method in Comparative Example 1 is 14.2±1.8%, and the average size of δ phase is about 18.6±3.3μm. It can be seen that, compared with Comparative Example 1, the high-carbon nickel-based superalloy prepared in the application effectively reduces the existence of Laves precipitated phase Nb-rich region, and reduces the size and volume fraction of δ phase precipitated in subsequent heat treatment, thereby improving the mechanical properties of the high-carbon nickel-based superalloy.

[0103] (6) Figure 11 is the analysis diagram of the as-cast microstructure of the nickel-based superalloy prepared in Comparative Example 3.

[0104] From Figure 11 It can be seen that the volume fraction of Laves phase of the as-cast microstructure of the nickel-based superalloy prepared in Comparative Example 3 is 8.9-10.1%.

[0105] (7) Figure 12 is the analysis diagram of the heat-treated microstructure of the nickel-based superalloy prepared in Comparative Example 3.

[0106] From Figure 12 It can be seen that the volume fraction of δ phase of the nickel-based superalloy (0.06%C) prepared in Comparative Example 3 after heat treatment is 6.5-8.5%, and the average size is about 13.4±2.8μm, which is higher and larger than the volume fraction of δ phase after heat treatment in the high-carbon nickel-based superalloy (0.12%C) prepared in Example 1. The volume fraction of carbide precipitated phase in the nickel-based superalloy (0.06%C) prepared in Comparative Example 3 is 0.78-1.01%, and the average distribution interval is 40.3±0.9μm, but the carbide in the alloy prepared in Comparative Example 3 is less than the alloy casting (0.12%C) prepared by the conventional casting method in Comparative Example 1, and the size is smaller.

[0107] Although the above embodiments have been described in detail, it should be understood that these are only some embodiments of the present application but not all the embodiments. Other embodiments can be obtained according to the above embodiments without creativity, and these embodiments all belong to the protection scope of the present application.

Claims

1. A high carbon nickel-based superalloy characterized in that, 0.10~0.12% C, 17~21% Cr, 50~55% Ni, 0.2~0.8% Al, 0.65~1.15% Ti, 0.04~0.35% Zr, 2.8~3.3% Mo, 4.5~5.5% Nb, 0.002~0.006% B, and the balance of Fe; The volume fraction of the δ phase in the high-carbon nickel-based superalloy is 2~2.4%, the average size of the δ phase is 6.6~7.8 μm, the volume fraction of the Laves precipitated phase is 1.7~1.9%, the volume fraction of the carbide precipitated phase is 1.48~2.17%, and the average distribution interval between the carbide precipitated phases is 24±8 μm; The porosity of the high-carbon nickel-based superalloy is ≤1%, and the grain size of the alloy is 78~118 μm; The matrix structure of the high-carbon nickel-based superalloy is a face-centered cubic austenite phase composed of nickel, iron and chromium, with a volume fraction of 70~80%, the volume fraction of the strengthening phase Ni3Nb is 10~20%, and the volume fraction of the strengthening phase Ni3Al is 1~3%; The preparation method of the high-carbon nickel-based superalloy comprises the following steps: After rough refining and refining of the high-carbon nickel-based alloy ingot under vacuum, the obtained melt is poured into a mold shell to perform directional thermal controlled solidification, thereby obtaining a solidified alloy; After cooling the solidified alloy to room temperature, the high-carbon nickel-based superalloy is obtained by sequentially performing homogenization heat treatment, solid solution heat treatment and aging heat treatment; The directional thermal controlled solidification is to pull the mold shell containing the melt from a hot zone to a cold zone, perform slow cooling in the hot zone, and perform rapid cooling in the cold zone; the temperature of the hot zone is 1290~1300 ℃; the temperature of the cold zone is 100~300 ℃; the cooling rate of the slow cooling in the hot zone is 0.16~0.18 ℃ / s; and the cooling rate of the rapid cooling in the cold zone is 5~10 ℃ / s.

2. A method of producing a high carbon nickel-based superalloy as claimed in claim 1, characterized in that, comprises the following steps: After rough refining and refining of the high-carbon nickel-based alloy ingot under vacuum, the obtained melt is poured into a mold shell to perform directional thermal controlled solidification, thereby obtaining a solidified alloy; the element composition of the high-carbon nickel-based alloy ingot is the same as that of the high-carbon nickel-based superalloy in claim 1; After cooling the solidified alloy to room temperature, the high-carbon nickel-based superalloy is obtained by sequentially performing homogenization heat treatment, solid solution heat treatment and aging heat treatment; The directional thermal controlled solidification is to pull the mold shell containing the melt from a hot zone to a cold zone, perform slow cooling in the hot zone, and perform rapid cooling in the cold zone; the temperature of the hot zone is 1290~1300 ℃; the temperature of the cold zone is 100~300 ℃; the cooling rate of the slow cooling in the hot zone is 0.16~0.18 ℃ / s; and the cooling rate of the rapid cooling in the cold zone is 5~10 ℃ / s.

3. The preparation method according to claim 2, characterized in that, The rough refining is to increase the temperature from room temperature to 1400~1600 ℃, and the temperature increasing time is 20~40 min; and the refining is to keep the temperature at 1500~1600 ℃ for 2~4 min.

4. The preparation method according to claim 2, characterized in that, Before the pouring, the mold shell is preheated, the preheating temperature of the mold shell is 1290-1300 DEG C, and the pouring speed is 0.5-0.8 kg / s.

5. The preparation method according to claim 2, characterized in that, The homogenizing heat treatment is performed at a temperature of 1050-1150 DEG C for 1.5-2.5 h.

6. The preparation method according to claim 2, characterized in that, The solid solution heat treatment is performed at a temperature of 950-955 DEG C for 1.5-2 h.

7. The preparation method according to claim 2, characterized in that, The aging heat treatment is performed in the following steps: first, first-stage aging heat treatment is performed, then, second-stage aging heat treatment is performed after first cooling, and finally, the second cooling is performed to room temperature; the first-stage aging heat treatment is performed at a temperature of 720-730 DEG C for 7-8 h; the first cooling is performed at a rate of 50-56 DEG C / h; The second-stage aging heat treatment is performed at a temperature of 620-630 DEG C for 7-8 h; and the second cooling is performed at a rate of 40-50 DEG C / min.

8. The use of the high-carbon nickel-based superalloy of claim 1 or the high-carbon nickel-based superalloy prepared by the method of any one of claims 2-7 in aerospace components.

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